Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONTINUOUS FLOW DRYER HAVING AT LEAST TWO SECTIONS
Background of the Invention
The invention relates to a continuous flow dryer for drying a material by
means of hot
air in at least two sections which are successively passed through by the
material
and largely separated in terms of air flow.
The invention relates further to a continuous flow dryer for drying a material
by
means of hot air with a first and a second section through which are passed
largely
by the material in a transport direction, in which an air supply device for
supplying
fresh air to the second section is provided, and an exhaust air recirculation
device for
removing exhaust air from the first section.
A continuous flow dryer is a dryer in which material to be dried is
transported through
the dryer continuously or in batches. Such a dryer is in particular a belt
dryer which
conveys the material to be dried through the continuous flow dryer. The
material to
be dried, for example, clarification sludge, wood chips, RDF (refuse-derived
fuel),
SSW (solid shredded waste), MSW (municipal solid waste), household waste,
grass
or agricultural products and by-products such as sugar beat pulp is in this
case firstly
moist or wet. The material is dried, during which moisture is removed by means
of
hot air. The hot air is specially produced by heating in particular air from
the
surroundings of the continuous flow dryer. On heating the air the relative
humidity of
this air falls, the air becomes "dryer". This hot air with lower relative air
moisture then
flows through in the continuous flow dryer the material to be dried or flows
around its
constituents. The material to be dried is at the same time conveyed in a
transport
direction through the through-flow dryer and at the same time flows through at
least
two sections. The individual section subdivides the through-flow dryer
spatially. The
sections are largely separated from one another in terms of air flow.
Thus, in the sections, different air flows are possible, which each have
different
relative air moistures and different temperatures. For heating the air to hot
air,
energy is naturally required. This energy is lost when the hot air produced
after the
drying of the material is released into the surroundings after the drying of
the
material. First approaches are therefore known for recirculating the hot air.
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In the through-flow dryer relevant here the heated air from the surroundings
is
supplied to the second section by means of an air supply device. This fresh
air is
cooled after flowing through the second section by taking up moisture from the
material to be dried and is enriched with water and thus forms exhaust air.
The
exhaust air is nevertheless recirculated from the second section into the
first section
as supply air. This recirculated supply air then flows through the first
section. On
further flowing through, the material to be dried releases further moisture to
this air.
This air becomes further saturated and then is led out of the first section by
means of
an exhaust air device.
The sections are thus very largely separated such that in them different air
flows are
possible, which can each have different relative moisture and different
temperature.
For heating the supply air as hot air, energy is of course required. This
energy is lost
when heated hot air is discharged into the surroundings of the through-flow
dryer
after drying the material. Therefore, as explained above, it is fundamentally
desired
to recirculate generated hot air as far as possible through many sections.
Object of the Invention
The object on which the invention is based is to create a through-flow dryer
for
drying a material by means of hot air which makes possible a further energy
saving
compared with known through-flow dryers.
Solution According to the Invention
This object is achieved according to the invention with a through-flow dryer
for drying
a material by means of hot air with a first and a second section, through
which
material is passed successively in a transport direction and largely separated
in
terms of air flow. Furthermore, a fresh air supply device is provided for
supplying
fresh air as first supply air into the first section, an exhaust air
recirculating device is
provided for discharging exhaust air from the second section and for
recirculating
exhaust air as second supply air back into the second section, and a heat
exchanger
is provided, through which on the one hand the fresh air and on the other hand
the
exhaust air are led for transmitting waste heat of the exhaust air into the
fresh air.
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In the through-flow dryer according to the invention, there is provided a
fresh air
supply device which supplies generally dry fresh air taken from the
surroundings as
first supply air to the through-flow dryer. At the through-flow dryer
furthermore an
exhaust air recirculating device leads exhaust air from a drying process out
of the
second section. This exhaust air is at least partly recirculated into the
second section
of the through-flow dryer. The exhaust air is in this case led according to
the
invention to a heat exchanger, at which thermal energy or waste heat is
transferred
from the exhaust air to the first supply air likewise flowing through the heat
exchanger. The two flows of exhaust air and first air are in this case
separated from
one another at the heat exchanger in particular by means of a separating
surface. At
the separating surface, then on its one side the exhaust air flows along and
on its
other side the first supply air flows along. Through the separating surface,
heat
energy of the exhaust air is discharged to the fresh air. The waste heat of
the
exhaust air heats thus heats the fresh air supplied to the through-flow dryer
and heat
energy from the exhaust air is recovered. At the same time the air flows of
exhaust
air and first supply air are separated from one another in terms of moisture.
The
moisture contained in the exhaust air cannot therefore pass into the first
supply air.
Advantageously the heat exchanger according to the invention is dimensioned
such
that moisture condenses out from the exhaust air on it. Moisture condenses out
when the relative air moisture of the respectively relevant air has reached
100% (in
words: one hundred per cent). The relative air moisture in air increases when
the air,
as in this case, cools. On the other hand, the relative air moisture decreases
when
the air is heated. These physical effects of the increase and decrease of the
air
moisture are shown in the Mollier-h,x diagram. The condensing out striven for
according to the invention is preferably achieved by the fact that the
separating
surface of the heat exchanger is dimensioned such that moisture from the
exhaust
air condenses out on it. For this, the exhaust air discharges so much thermal
energy
to the separating surface that the relative moisture in the exhaust air 100%
(in words:
one hundred per cent) is achieved. The heat exchanger according to the
invention
thus has advantageously three functions. The first function is the
dehumidifying of
the exhaust air which flows through the heat exchanger. The second function is
the
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heating of the supplied fresh air. The third function is the reducing of
relative air
moisture of the supplied fresh air, caused by the heating of this fresh air.
According to the invention, preferably furthermore a first heater is provided
for
heating the first supply air before it is supplied into the first section. A
heater heats
air by means of energy supply. The heater is, for example, a hot water heat
exchanger, a steam heat exchanger, an electric heating device or a heat
burner. On
heating the air with the heater, this supply air decreases, as already
mentioned
above, the relative air moisture of this supply air. A low air moisture is
advantageous,
since the such supply air can then take up more water. Warmer supply air can
thus
take up colder supply air. This first supply air is, according to the
invention, supplied
to the first section. In this first section the moisture of the material to be
dried is still
at its greatest in terms of its conveying direction. Therefore, it is
particular
advantageous if the take-up capacity of water of the supplied air is high in
this
section.
Furthermore, advantageously a second heater is provided for heating the second
supply air before it is recirculated into the second section. As already
described, the
relative air moisture of air decreases when it is heated. A second heater
which heats
the second supply air thus decreases likewise the relative moisture in this
second
supply air and increases the temperature of the second supply air. A low
relative air
moisture in the second supply air is in particular then of advantage when
comparatively low residual moisture is to be removed from the material to be
dried in
the second section.
Preferably, the exhaust air supply device is furthermore provided with a
recirculating
line which serves for direct recirculating of exhaust air from the second
section as
circulating air back into the second section. The exhaust air recirculating
device then
leads exhaust air from the second section directly and without intermediate
handling
back into the second section. The directly recirculated exhaust air from the
second
section is mixed with the second supply air supplied there, which accordingly
has the
result that a mixture of treated supply air and untreated supply air flows
into the
second section. This mixture has a mixing temperature and a mixing air
moisture.
Thus, the supply air is colder and dryer and the exhaust air is warmer and
more
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moist. Advantageously the air can be very cold and very dry because it is
directly
heated by the albeit also moist, but warm component of the recirculated
exhaust air.
Furthermore, with this direct recirculation a particularly simple control of
the moisture
and of the temperature of the air in the second section is possible.
According to the invention, preferably at least two regions or subsections are
provided in the second section which are largely separated in terms of air
flow and
the exhaust air of the two regions is collected by the heat exchanger in a
guided
manner. The second section is in this way for its part further subdivided, in
fact into
at least a first and a second region. These regions are connected in series
successively in the transport direction. The respective region generally has
its own
temperature and its own relative moisture of the air flow inside this region.
Advantageously this temperature and the relative moisture is adapted to the
prevailing moisture conditions of the material to be dried there in each case.
Exhaust
air to be led away from the respective regions is brought together and led
jointly to
the heat exchanger. Advantageously, with the collecting of the exhaust air an
exhaust air mixture forms. The exhaust air mixture has a largely uniform,
common
relative air moisture and a mixing temperature. Particularly advantageously,
in this
case not only for each individual region does a separate heat exchanger have
to be
provided, but in particular a single heat exchanger for the entire exhaust air
to be
discharged from the plurality of regions is sufficient.
Advantageously, furthermore in at least one of the sections and/or regions an
exhaust air second is provided, by means of which in the exhaust air its
moisture is
to be determined. Such an air sensor determines in particular the relative air
moisture and/or the temperature of the air flowing to or around it.
Advantageously,
the relative air moisture of the exhaust air is thus to be determined by means
of the
exhaust air sensor. If the relative moisture of the exhaust air is known, it
can be
defined by means of a control whether this exhaust air is to be dehumidified
or
whether this air is to be supplied again directly to the respective section or
the
respective region.
Alternatively or additionally, furthermore there is provided a supply air
sensor, by
means of which moisture in the supply air is to be determined. The supply air
sensor
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determines the relative air moisture of the on-flowing supply air.
Advantageously it
can thus be determined the relative air moisture with which the supply air
flows into
the respective section. Particularly advantageously, it can thus also be
determined
whether and by how many degrees Celsius the supply air is to be heated up
additionally by a heater, in order to achieve a desired relative air moisture
in the
supply air.
In a preferred manner, furthermore for transporting the material through the
through-
flow dryer two belts are provided, which are assigned in particular to the
first section
and the second section. Such a two-part belt in a continuous flow dryer
enables each
of the two sections to have a belt of their own. Thus, the two sections can
also be
arranged spatially separated from one another, in particular one above the
other.
According to the invention, preferably the transport direction is directed
from the
second section to the first section. Such a transport direction is thus not
orientated
from the first section to the second section, but vice versa. Such a transport
direction
in the "opposite direction" makes it possible to dry the material lastly with
supplied
fresh air. This is particularly advantageous when the material is to be dried
lastly with
particularly pure air. As a further advantage, in this transport direction the
second
heater is designed small for heating the second supply air. Particularly
advantageously this heater can be omitted.
Furthermore, advantageously also a regulating device is provided, by means of
which the moisture in the exhaust air is to be measured and an air guidance in
the
exhaust air recirculation device is to be regulated. A regulating device or
control
evaluates inputs of the regulating device and regulates or controls by means
of logic
of the regulating device its outputs. As inputs here serve electrical signals
of sensors
of various kinds, such as for example a temperature sensor or a moisture
sensor. As
outputs serve mostly switches or electrical signals, for example for
controlling the
heater. By means of the regulating device, the air guidance is advantageous,
in
particular by means ventilation, in the exhaust air recirculation device at
the
respectively prevailing relative moisture of the exhaust air.
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A method according to the invention for operating a through-flow dryer for
drying a
material by means of hot air with a first and a second section which are
passed
through successively by material in a transporting direction and are largely
separated
in terms of air flow, is designed with the steps: supplying fresh air as first
supply air
into the first section, and discharging of exhaust air from the second
section, and
recirculating exhaust air from the second section, and recirculating exhaust
air as
second supply air back into the second section and transmitting exhaust heat
of the
exhaust air into the fresh air.
This object is further achieved according to the invention with a through-flow
dryer
for drying a material by means of hot air with a first and a second section,
through
which the material is passed in a transport direction and are largely
separated,
wherein an air supply device for supplying fresh air to the second section, an
exhaust air recirculation device for supplying fresh air to the second
section, an
exhaust air recirculation device for recirculating exhaust air from the second
section
into the first section as supply air and an exhaust air discharging device for
discharging waste air from the first section are provided. Furthermore,
according to
the invention the air supply device is designed with a heat exchanger, through
which
the fresh air and the exhaust air are guided from the first section.
In the through-flow dryer according to the invention, an air supply device is
provided,
which supplies fresh air taken from the surroundings to a heat exchanger. The
heat
exchanger has in this case flowing through on the one hand fresh air and on
the
other hand recirculated exhaust air of the through-flow dryer is conveyed
through the
heat exchanger before at least two sections. The exhaust air thus recirculated
has a
high moisture content. It cools down on the heat exchanger and the water
contained
therein flows out. By means of the heat exchanger according to the invention
on the
one hand the supply air is warmed up and on the other hand however the exhaust
air
is also at the same time dehumidified.
The two air flows according to the invention are in this case in particular at
the heat
exchanger separated from one another by means of a separating surface. At the
separating surface, there then flows past on the one side the exhaust air and
on the
other side the fresh air. By means of the separating surface the heat
exchanger
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transmits a thermal energy or heat from the exhaust air to the fresh air.
Thermal
energy is transmitted from the exhaust air to the fresh air. A "thermal
recovery" takes
place. The fresh air is heated by means of the waste heat of the exhaust air.
Owing
to the heating the relative air humidity of the fresh air decreases, the fresh
air
becomes "dryer". The fresh air is at the same time separated in terms of
moisture.
The moisture or liquid in the exhaust air can therefore pass over to the fresh
air.
According to the invention, preferably the air supply device is designed such
that the
exhaust air from the first section is led out of the first section from the
through-flow
dryer as outgoing air. From the through-flow dryer there is led at only one
place
fresh air into the through-flow dryer and only at one place is outgoing air is
led out of
the continuous flow dryer. The through-flow dryer can thus be advantageously
equipped with only a single heat exchanger, through which both fresh air and
also
outgoing air of the through-flow dryer are led.
Advantageously, the air supply device according to the invention is designed
with a
first heater for heating the supply air before it is supplied to the first
section. A heater
heats by means of energy supply the air flowing through it. The heater is, for
example, an electric heating device, a heat burner or a heat register through
which
flows heating fluid. On the heating of the air by means of the heater the
relative air
moisture falls. A low air moisture is advantageous on drying, since then in
particular
the fresh air heated in this manner can take up more moisture or water. The
heated
supply air is according to the invention of the second section, therefore
supplied
preferably with a section at the rear in the transporting direction or a
section
arranged further behind than the first section. In this second section the
relative
moisture of the material to be dried is, with respect to its conveying
direction,
comparatively low. Therefore it is particularly advantageous if the take-up
capacity of
water of the fresh air supplied in this section is particularly high.
According to the invention, preferably the exhaust air recirculating device is
designed
with a second heater which serves for heating the supply air before it is
supplied to
the second section. With the second heater preferred according to the
invention, the
supply air is further heated before the supply into the second section is
further
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heated. Thus, it is possible in the second section to particularly highly
reduce the
relative moisture of the material dried there.
In a preferred manner furthermore a supply air sensor is provided, by means of
which in the air downstream or before the heater its moisture can be
determined.
The supply air sensor determines the relative air moisture of the on-flowing
supply
air. Advantageously, it can thus be determined with which relative air
moisture the
supply air flows into the respective section. Particularly advantageously it
can thus
also be determined whether and by how many degrees Celsius the supply air can
be
heated additionally by means of a heater, in order to achieve a desired
relative air
moisture in the supply air.
According to the invention, preferably furthermore the exhaust air
recirculation
device is designed with a fan, for controlled recirculating of air through the
exhaust
air recirculation device. The fan sucks in particular air from the section
associated
with it and leads this air back to the following section. By means of the fan,
it is in this
case controlled how much air is sucked out of the respective section and
preferably
then is also led on to the following exhaust air recirculation device.
Particularly
preferably there is also provided a fan at or on the exhaust air recirculation
device,
since this brings about a particularly uniform distribution of the air
conveyance
through the respective sections.
In a preferred manner the first section is furthermore subdivided into at
least two
regions, each of which is assigned an exhaust air recirculation device for
recirculating exhaust air from the upstream region into the respectively
following
downstream. The regions form in this case an air flow subdivision of the first
section.
This subdivision or separation has the effect that the individual regions for
their part
can have different temperatures and moistures. The regions thus form a kind of
"series connection", in which the exhaust air is recirculated from the
preceding region
into the respective following region. Particularly advantageously, a plurality
of almost
identical regions are thus coupled to one another. By means of this
arrangement of a
plurality of following regions, the through-flow dryer according to the
invention is
simply scalable with regard to its power and size.
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Furthermore advantageously the transport direction of the transport belt is
designed
either directed from the first section to the second section or from the
second section
to the first section. A transport direction of the transport belt from the
first section to
the second section has the effect that moist or wet material is pre-dried from
the first
section by means of the exhaust air of the second section. Subsequently, the
pre-
dried material in the second section is post-dried by means of the supplied
fresh air.
This transporting direction is advantageous particularly when the material at
the end
of its transporting path is to be dried as much as possible. It is preferable
however
for the transport direction of the transport belt to be guided by the second
section to
the first section. This transport device is then particularly advantageous
when on the
pre-drying particularly a lot of moisture can be removed. Preferably,
according to the
invention a regulating device is provided, by means of which the exhaust air
recirculating device can be controlled. A regulating device or control
evaluates inputs
and regulates or controls outputs by means of logic. As a rule, electrical
signals of
sensors of varying manner, such as for example a temperature sensor or a
moisture
sensor serve as inputs. As outputs serve mostly switches or electrical
signals, for
example for controlling the preferred heater or electrical signals, for
example for
controlling the preferred heater or fan.
A further method according to the invention for operating a through-flow dryer
for
drying a material by means of hot air with a first and a second section,
through which
material can be successively passed through in a transport direction and in
terms of
air flow are largely separated, is designed with the following steps:
supplying fresh
air as supply air into the second section, discharging exhaust air from the
second
section, supplying exhaust air as first supply air into the first section and
discharging
exhaust air from the first section. In this case, thermal energy of the
exhaust air is
transmitted to the fresh air by means of a heat exchanger.
Brief Description of the Drawings
An exemplary embodiment of the solution according to the invention is
explained in
greater detail with the aid of the appended schematic drawings, in which:
Fig. 1 shows a highly simplified longitudinal section of a through-flow dryer
according
to the prior art,
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Fig. 2 shows a highly simplified longitudinal section of a through-flow dryer
according
to the invention,
Fig. 3 shows a highly simplified longitudinal section of a through-flow dryer
according
to the invention, which is equipped with a regulating device, and
Fig. 4 shows a highly simplified longitudinal section of a through-flow dryer
according
to the invention, which is according to the prior art,
Fig. 5 shows a highly simplified longitudinal section of a through-flow dryer
according
to the invention,
Fig. 6 shows a highly simplified longitudinal section of a further through-
flow dryer
according to the invention, which is according to the prior art, having three
regions,
and
Fig. 7 shows a through-flow dryer according to Fig. 6, which is equipped with
a
regulating device.
Detailed Description of the Exemplary Embodiment
Figs. 1 to 3 each show a through-flow dryer 10 in the form of a belt dryer.
The
through-flow dryer 10 has a housing 12, through which firstly moist or wet
material
14 is to be transported through by means of a belt 16 in a transport direction
18. The
material 14 passes through during the transporting a first section 20 and a
second
section 22. The two sections 20 and 22 subdivide the housing 12 spatially.
Inside the
housing 12 there is situated furthermore hot air 24 which removes moisture
from the
material 14 (not shown) to be dried. With the removal of moisture from the
material
14 the material becomes dryer, it is dried.
Fig. 2 and 3 illustrate how in the exemplary embodiments there the hot air 24
is
produced. For this fresh air flows from outside the housing 12, conveyed by a
fresh
air supply device 28, into the housing 12. The fresh air in this case flows
through a
first heater 30. The first heater 30 heats the fresh air 26 on its way through
the
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heater 30. With the heating of the fresh air 26 the relative air moisture
decreases, the
fresh air 26 becomes "dryer".
This fresh air 26 after heating is referred to as first supply air 32. The
first supply air
32 flows into the first sector 20 and flows around there the individual
particles of the
material 14 or flows through the layer of the material 14 on the belt 16. On
this
flowing-around of the particles of the material 14 the first supply air 32
takes up
moisture from the material 14. The relative air moisture of the first supply
air 32 takes
up moisture from the material 14. The relative air moisture of the first
supply air 32
increases, the first supply air 32 becomes "dryer". The moistened supply air
32 is
subsequently removed from the first section 20 as first exhaust air 34 from
the
housing 12 into its surroundings. This exhaust air thus constitutes outgoing
air.
After the first section 20 the material flows through the second section 22.
This
second section is for its part subdivided into two regions 36, 38. The two
regions 36,
38 are connected in series and separated largely from one another in terms of
air
flow. Alternatively to the exemplary embodiments shown, the second section 22
can
also be subdivided into more than two regions 36, 38, in particular three,
four or five
regions.
At both regions 36, 38 in each case a second exhaust air 40 is led out and in
each
case a second supply air 42 is supplied. The second supply air 40 is led back
into
the respective region by means of an exhaust air recirculation device 44
partly
directly as second supply air 42 into the respective region. Before the
supplying of
the second supply air 42 into the respective region 36, 38, in each case a
second
heater 46 is provided. The second heater 46 heats the second supply air 42,
whereby the relative moisture of the second supply air 42 falls.
The exhaust air recirculation device 44 comprises a recirculation line 48,
through
which likewise the exhaust air 40 flows. This recirculation line 48 has a
branch 50
and a supply 52. At the branching 50 a part of the exhaust air is branched off
and by
means of a line is led into a collecting line 56. The collecting line 56, in
Fig. 3, or the
line 54, in Fig. 2, comprises preferably a regulated or controlled fan 57. The
collecting line 56 collects the exhaust air 40 branched off from the first and
second
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region 36, 38 and leads this exhaust air to a heat exchanger 58. The heat
exchanger
58 is arranged in front of the first heater 30 in the fresh air supply device
28.
The exhaust air 40 flows through the heat exchanger 58 and at the same time
the
fresh air 26 flows through this heat exchanger 58. The exhaust air 40 and the
fresh
air 26 are thus separated from one another by means of a separating surface 60
shown symbolically in Fig. 2 and 3. Via this separating surface 60 the exhaust
air 40
and the fresh air 26 exchange heat and thermal energy. Since the exhaust air
40 is
generally warmer than the fresh air 26, the fresh air is normally heated by
means of
the heat from the exhaust air 40. The heat of the exhaust air 40 given off is
here
referred to as waste heat 62. The giving off of the heat 62 has the result
that the
exhaust air 40 cools. How much waste heat 62 the exhaust air 40 gives off on
passing through the heat exchanger 58 depends on the area and the heat
permeability or the heat transition coefficient of the material.
The area and the heat permeability of the separating surface 60 are chosen in
the
exemplary embodiments of Figs. 2 and 3 such that the exhaust air 40 flowing
through is at the same time dehumidified. This means that at the separating
surface
60 the exhaust air 40 is cooled to such an extent that there a relative air
moisture of
100% (in words: one hundred per cent) prevails. At the separating surface 60
water
64 or moisture then separates out from the exhaust air 40. With the separating-
out of
water 64 at the separating surface 60, the water 64 is withdrawn from the
exhaust air
40, the exhaust air 40 becomes dryer.
The water 64 flows off as water from the heat exchanger 58 and the dryer,
cooler
exhaust air 40 is led by means of a supply line 66 to the second section 22.
At the second section 22 the supply line 66 separates into two lines 68. The
supply
line 66, shown in Fig. 3, or the line 68, shown in Fig. 2 can advantageously
comprise
a fan 69. This fan 69 is in this exemplary embodiment able to be regulated
with
regard to its speed and act as sucking. The lines 68 connect in a flowing line
the
supply line 66 with the supply line 52 of the respective region 36, 38. The
exhaust air
40 is thus fed into the recirculation line 48 by means of the supply line 52.
Within the
recirculation line 48 there forms at the supply line 52 a mixture of supplied
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dehumidified, colder exhaust air 40 and moist warm exhaust air 40 from the
recirculation from the respective region 36, 38. This mixture of the exhaust
air 40
flows through the second heater 46 as second supply air 42 into the respective
regions 36, 38 of the second section 22.
In order to regulate the air flows of the exhaust air 40 and of the supply air
42 in the
respective lines, the through-flow dryer 10 comprises according to Fig. 3 a
regulating
device 70. The regulating device 70 is operatively coupled with a plurality of
exhaust
air sensors 72 and to a plurality of supply-air sensors 74.
The individual exhaust air sensor 72 measures in the exhaust air 40 from the
second
section 22 in each case region 36, 38 the relative air moisture. Depending on
the
relative air moisture of the exhaust air 40 the regulating device 70 then
regulates the
separation of the exhaust air 40 in the region of 90 to 100% (in words: ninety
to one
hundred per cent), in particular 95 to 100% (in words ninety-five to one
hundred per
cent), exhaust air 40 is led increased to the heat exchanger 58 and the heat
exchanger at the heat exchanger dehumidified.
The only supply air sensor 74 measures in the supply air 42 to the respective
region
36, 38 of the second section 22 the relative air moisture in the flow
direction after the
supply 52 and before the second heater 46. Depending on the relative air
moisture of
the supply air 42, the regulating device 70 regulates the admixing of the
exhaust air
40 at the supply 52.
In an alternative exemplary embodiment, not illustrated, the exhaust air
sensor 72
and the supply air sensor 74 can additionally measure the temperature
prevailing
there.
Figs. 4 to 7 show in each case a through-flow dryer 110 in the form of a belt
dryer.
The through-flow dryer 110 comprises a housing 112, through which firstly
moist or
wet material 114 is to be transported by means of a transport belt 116 in a
transporting direction 118. The material 114 passes through, on this
transport,
successively firstly a first section 120 and then a second section 122, which
subdivide the housing 112 spatially. In each of the sections 120, 122, hot air
is
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,
situated inside the housing 112. The respective hot air 124 of the individual
sections
120, 122 is largely separated in terms of air flow. The hot air 124 withdraws
in each
of the sections the moisture 120, 122 from the material 114 or liquid 126
transported
therein, in particular water. The removal of liquid 126 from the material 114
dehumidifies the material 114. The material 114 becomes dryer or is dried.
The exemplary embodiments in Figs. 5 to 7 show the air guidance according to
the
invention of the hot air 124 in the sections 120 and 122. The hot air 124 for
the
second section 122 is generated in an air supply device 128 by means of a heat
exchanger 130 and a heater 132. The heat exchanger 130 and the heater 132 in
this
case heat fresh air 134 from the surroundings and lead it into the second
section
122. From the second section an exhaust air recirculation device 136 leads
back
"used" fresh air 134 as exhaust air 138 from the second section 122 into the
first
section 120 as supply air 140 for the first section 120. This supply air 140
is in the
first section 120 further moistened by the material 114 present therein and
then by
means of an exhaust air recirculation device 142 is led out of the first
section 120
and discharged as outgoing air 144 to the surroundings of the through-flow
dryer
110.
In order that a heat energy 146 contained in the outgoing air 144 is not
discharged
unused into the surroundings, the exhaust air 138 is conveyed to the heat
exchanger
130 of the air supply device 128 by means of the exhaust air recirculation
device
142. The exhaust air 138 becomes outgoing air after flowing through the heat
exchanger 144.
The heat exchanger 130 of the air supply device 128 thus at the same time has
the
exhaust air 38 and the fresh air 134 flowing through it. The exhaust air 138
and the
fresh air 134 are in this case in terms of flow separated by means of an
exchange
surface 148 and separating surface. This exchange surface 148 transmits the
heat
energy 146 of the exhaust air 138 to the fresh air 134. In order to heat the
fresh air
134 further, in the flow direction of the fresh air 134 after the heat
exchanger 130 the
heater is arranged, before the fresh air 134 then flows into the second
section 122.
In the second section 122 the fresh air 134 flows around and through the
material
114 and the transport belt 116 of the transport device 118. On flowing around
the
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16
material 114 the fresh air 134 takes up the liquid 126 contained in the
material 114.
The fresh air 134 is enriched with water or becomes more moist.
From the second section 122 the fresh air 134 flows out by means of the
exhaust air
recirculation device 136 as exhaust air 138. The exhaust air recirculation
device 136
comprises a fan 150 and a heater 152. The fan 150 sucks the exhaust air 138
out of
the second section 122 and leads it through the heater 152 into the first
section 120.
The heater 152 heats the exhaust air 138 in doing so. With the heating the
relative
air moisture of the first exhaust air 138 falls, it is thus processed or "more
receptive".
The first exhaust air 138 becomes thereby supply air 140.
The supply air 140 flows through in Fig. 5 the first section 120 and in doing
so takes
up likewise liquid. By means of the exhaust air recirculation device 142 which
comprises a fan 150, the exhaust air 138 is then discharged to the
surroundings from
the first section 122 after flowing through the heat exchanger 130 as outgoing
air
144.
Fig. 6 and Fig. 7 show an exemplary embodiment of a through-flow dryer 110, in
which the first section is subdivided into a first region 154, a second region
156 and
a third region 158.
The second and third region 156, 158 are intermediate members between the
second section 122 and the first region 154. The regions 154, 156, 158 form a
"series circuit". In both regions 156, 158 supply air 140 is supplied by the
region
following in the transport direction 118 by means of a respective
recirculation device
136. The supply air 140 flows through the respective region 156, 158. After
flowing
through, this "used" supply air 140 is recirculated as exhaust air 138 by
means of a
recirculation device 136 in the transport direction 118 in the respectively
preceding
regions 154, 156. These exhaust air recirculation devices 136 also comprise in
each
case a fan 150 and a heater 152. The fan 150 transports also here the exhaust
air
38 further and the heater heats this.
As shown in Fig. 7, the air supply device 128 and the exhaust air
recirculation device
136 is designed with in each case one supply air sensor 160, which is provided
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downstream in front of the respective heaters 132 and 152. The supply air
sensors
160 and the heaters 132 and 152 are operatively coupled to a regulating device
162,
for example a customary programmable logic controller (PLC). In addition, the
regulating device 162 is operatively coupled to the heaters 132, 152 and
additionally
or alternatively to the fans 150. The regulating device 162 regulates thus, by
means
of which signals determined by the supply air sensors 160 the respective
heaters
132 and 152. Depending on the embodiment of the regulating device 162,
additionally or alternatively the respective fans 150 are regulated.
Finally it should be noted that all the characteristics which are mentioned in
the
application documents and in particular in the dependent claims, despite the
formal
reference back to one or more specific claims, individually or in any
combination is
intended to have independent protection.
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18
List of reference symbols
through-flow dryer
12 housing
14 material
16 belt
18 transport direction
section
22 section
24 hot air
26 fresh air
28 fresh-air supply device
heater
32 supply air
34 exhaust air
36 region
38 region
exhaust air
42 supply air
44 exhaust air recirculation device
46 heater
48 recirculation device
branch
52 supply
54 line
56 collecting line
57 fan
58 heat exchanger
separating surface
62 waste heat
64 water
66 supply line
68 line
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69 fan
70 regulating device
72 exhaust air sensor
74 supply air sensor
110 through-flow dryer
112 housing
114 material
116 transport belt
118 transport direction
120 first section
122 second section
124 hot air
126 liquid
128 air supply device
130 heat exchanger
132 heater
134 fresh air
136 exhaust air recirculation device
138 exhaust air
140 supply air
142 exhaust air recirculation device
144 outgoing air
146 thermal energy
148 exchange surface
150 fan
152 heater
154 region
156 region
158 region
160 supply air sensor
162 regulating device
